Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer sheets that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass often refers to a transparent laminate comprising a poly(vinyl butyral) sheet disposed between two sheets of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening or the dispersion of shards of glass, thus minimizing damage or injury to the objects or persons within an enclosed area. Safety glass also can be used to provide other beneficial effects, such as to attenuate acoustic noise, reduce UV and/or IR light transmission, and/or enhance the appearance and aesthetic appeal of window openings.
An important consideration for the formulation of the thermoplastic interlayer is the sound transmission character of the finished product. Generally it is desirable to use interlayers that reduce the level of outside noise that is transmitted through the glass. A conventional single polymer sheet interlayer that has been modified to improve sound performance will usually have one or more physical characteristics modified in order to reduce the percentage transmission of sound through the glass. Conventional attempts at such acoustic dampening have included using thermoplastic polymers with low glass transition temperatures. Single sheet interlayers that have been formulated to improve sound transmission characteristics, however, are typically difficult to handle and are limited in the compositional variations that can be pragmatically employed.
Recent attempts to improve sound transmission characteristics while also maintaining manageability of the interlayer have involved using multiple polymer sheet layers in place of the conventional single polymer sheet interlayer. For example, two adjacent layers of thermoplastic polymer have been employed where the layers have dissimilar characteristics (see, for example U.S. Pat. Nos. 5,340,654 and 5,190,826, and U.S. Patent Application 2003/0139520 A1).
Unfortunately, the advent of multiple layer interlayers has resulted in the reemergence of challenges that had been overcome for single layer interlayers. For example, while incorporation of a colored gradient into a thicker, single polymer sheet interlayer has been known for some time (see, for example, U.S. Pat. Nos. 4,316,868 and 3,799,718), the incorporation of a colored gradient into a multiple layer interlayer having two or more thinner polymer sheets presents processing difficulties that can result in substandard appearance, stability, and/or glass adhesion in finished laminated glass products.
Further improved compositions and methods are needed to enhance the sound dampening characteristics of multiple layer glass panels, and specifically multiple layer glass panels comprising poly(vinyl butyral) layers, while allowing facile processing and without negatively impacting optical qualities.